Hydraulic power system



Sept. 9, 1941. K. w. FIEBER ET AL HYDRAULIC. POWER SYSTEM Filed Feb. 15,1938 IN VENTOR.

.2 a I bun 14 ATTORNEY.

Patented Sept. 9, 1941 2,255,560 HYDRAULIC rowan SYSTEM Karl WilfridFieber, Berlin-Charlottenburg, and

Oskar Wiirthner, Berlin-Wannsee,

Germany,

assignors to Siemens Apparate und Maschinen Gesellschaft mitbeschrankter Haftung, Berlin, Germany, a corporation of GermanyApplication February 15, 1938, Serial No. 190,650 In GermanyFebruary-20, 1937 Claims.

This invention relates to hydraulic power systems and more particularlyto apparatus comprising a plurality of pumping units which, incombination, are adapted to give a wide range of fluid pressures andfluid outputs.

Quite frequently in instances where a servomotor is used to overcomesome resistance, said resistance varies in magnitude over a wide range,as, for example, in the actuation by a servomotor of the collapsiblelanding gear of an airplane. Itis well known that, in order to retractthe' carriage of an airplane, it is necessary to apply a relatively lowpressure during the greater part of the retraction and a comparativelyhigh pressure at the very end of the retraction, and, if a single pumpdriven by an electric motor provides the fluid to the servomotor, thepumping unit, including the pump and electro-motor, must be designed tomeet the maximum demand of the servo-motor, i. e., the

demand at the end of the retraction. As a result, the pumping unitoperates at full load only during a fractional part of the total timethat it is used. It is accordingly an object of the present invention toprovide a novel hydraulic power unit which is adapted for use with aservo-motor demanding varying fluid pressures and which comprises aplurality of pumps, each of which operates at substantially full loadfor all pressure outputs'of the unit, thereby saving weight and spaceover a pumping unit comprising a single pump operating under similarload conditions. The decreased weightand size of the former is due tothe difference in capacity'of the electric motors necessary to drive thesaid power units.

Another object of the invention is to provide a novel power means forprocuring either a low fluid pressure with a large fluid output or agreater fluid pressure with a decreased output.

A further object of the invention is to provide novel automatic meansfor controlling the output of the above power unit in accordance withthe pressure demand thereon.

Still another object is to provide a novel hydraulic power unit which isparticularly adapted for actuating the retractable landing gear of an.airplane.

A still further object is to provide a novel supplementary feeder incombination with the abovehydraulic power means for the purpose ofmeeting any excessive demands for fluid pressure or fluid output uponsaid means.

The above and further objects and novel features of the invention willmore fully appear ever, that the drawing is for the purpose ofillustration only and is not intended to define the limits of theinvention, reference for this latter purpose being had primarily to theappended claims.

In the drawing, wherein like reference characters refer to like partsthroughout the several v1ews-- 1 Fig. l is a pressure curve showing thepressure demand upon the servo-motor of a retractable landing gearduring the collapsing of' the carriage, and i Fig. 2 is a diagrammaticrepresentation of one embodiment of the present invention.

In the single embodiment of the invention illustratedin the drawing,there is provided a hydraulic power unit comprising a plurality of fluidpumps and .a pressure responsive valve mechanism for controlling thefluid connection between the said pumps. The pumps are connected,depending upon the desired pressure output, either in parallel or inseries, 1. e., either as a group of single stage pumps operating betweenthe same pressure range or as a single pump comprising several stagesoperating be- I tween a greater pressure range. When the power intakeupon a predetermined pressure rise, when unit used, as, for example, tofeed a servomotor, the pumps initially operate in-parallel,

pumping a large quantity of low pressure fluid,

but when the pressure demand reaches a predetermined value, preferablywhen-the pumps become slightly overloaded, the valve mechanismcontrolling the connections between said pumps automatically rearrangessaid connections to cause the pumps to operate in series and theincreased pressure demand is readily met, al-

though the fluid output is proportionately decreased. A supplementaryfeeder and a valve mechanism controlling the operation/thereof are also.provided and ;are adapted try supply fluid to the motor, upon a drop ofpressure when the pumps are operating in either pressure range or inthealternative to supply fluid to the pump the pumps are connected inseries.

The pressure demand upon the novel hydraulic power system of the presentinvention by the servo-motor of a retractable landing gear unit, asshown in Fig. '1, is typical of the conditions under which said systemoperates most efllciently. When the carriage is to be retracted,

the pressure during the greater part a of the retraction does not exceed12. However, after the gear has been movedinto the airplane body, thepressure must necessarily be increased to terminally move the landinggear into full retractedor housed position and during this part b of theretraction, the pressure builds up considerably in excess of p. If thepressure exceeds that of the pumps operating in series and the demand isfor a still greater fluid pressure, the valve mechanism controlling thesupplementary feeder is automatically operated to introduce the saidfeeder into the fluid circuit to meet the demand.

In the embodiment illustrated'in 2, the

novel power system comprises a reservoir or source 4, from which fluidis adapted to flow into a conduit Sand through a valve mechanism f intothe fluid circuit of the said system. Nor-= mally, conduit 5 is directlyconnected by valve mechanism 6; with a conduit l and, when the powersystem is operating in the low pressure range, 1. e., below pressure 10,substantially onehalf of the fluid flows from conduit! to a conduit 8. 5The latter, as shown, is connected to the suction port of a rotary pump9, diagrammatically illustrated in the drawing. It will be understoodthat pumps 9 and H are of the type in which an increase in the inputpressure will cause a corresponding increase in its output pressure.

Pump 9 is preferably driven by an electric motor (not shown) and thehigh pressure fluid discharge therefrom flows into a conduit Ill andfrom said conduit through a control valve mechanism ll, then throughconduits I2 and l3 to a conduit l5.

A conduit l5, by which substantially one-half of the fluid flow throughconduit I from source 4. is diverted when the system is operating in thelow pressure range, causes the diverted portion ofthe fluid to passthrough valve mechanism II and into a conduit l6. Conduit I6 isconnected to the suction port of a pump II, which is of a similardesignto pump 9 and which is preferably driven by the same electric motor aspump 9. The discharge from pump ll flows into conduit Hi where itcombines with the high pressure discharge of pump 9, and the combineddischarge of J the two pumps flows into a servo-motor l8 to drive apiston l9 and operate, forexample, the

. retractable landing gear of an airplane. When operating in this.manner, the combined discharge of the pumps is the sum of the fluidoutputs of each of the pumps and the pressure of said discharge is equalto the pressure which a single pump is capable of producing.

When the resistance to the movement 01' piston I9 increases. to thepoint where the demand upon the pumps is for a fluid pressure equal toor greater than pressure p, the resulting increase in the pressuredischarge of the pumps in response to this demand actuates valvemechanism I l' and causes said mechanism to shut ofl conduits Ill and i6from conduits l2 and I5, respectively, and to connect the twofirst-named conduits to each other. The rearrangement of connections ispreferably eflectedby movement of a piston valve 20 in a casing or valvebody 2| of valve mechanism. As shown, said valve is adapted forreciprocal movement in said body and isnormally maintained in a positionto permit fluid flow from conduit in toconduit I2 and from conduit l5 toconduit l6 by suitable resilient means in the form of coil spring 22interposed between said body and the right end of said valve. A chamber23 between said body and the left end of said piston valve is connectedby channel 24 to the conduit l0 and, therefore, to the discharge side ofpump! and when the pressure in said chamber becomes great enough toovercome the resistive force of spring 22, valve 20 is moved thereby tothe right and simultaneously shuts off the connection between conduit Hiand conduit i2 and between conduit l5 and conduit l6 and opens aconnection between conduit is and conduit i6. Coil spring 22 may besuitably chosen so as to have the above movement occur. in response toany predetermined pressure and in the instance where the power system isutilized in combination with a retractable landing gear, therearrangement of connections between pumps 9 and i1 is made to occurwhen. the de mand begins to exceed the pressure p. The saidrearrangement of connections causes pumps it and Q to operate in seriesinstead of, as initially, in parallel and the discharge fluid of pump 9now feeds the suction intake of pump Ell providing a two-stage pumpingsystem which has an initial second stage) pressure equal to the finalpressure of the pumping unit, when operatingin said feeder is connectedto the high pressure or 1 I discharge side of said pumping units byconduits 26 and 21. Conduit 26 is connected at one end to the junctionof conduits i2 and i3 and at the I other end to valve mechanism 6, andconduit 2! pumps due perhaps to a greater demand upon,

movement to the right.

is connected from said valve mechanism to said supplementary feeder.piston 28 reciprocable in-a cylinder 29 and means, in the form of coilspring 30, interposed between the right end of said cylinder andtheright face of said piston, tendingto keep said piston from capacity ofthe left end of said cylinder is a function of the. pressure of thefluid flowingtherein through conduit 21 and when the pressure'o'f thepump discharge fluid in conduit I4 is equal to the pressure of the fluidwithin said cylinder end, there is no flow into or out of said cylinderthrough the conduit '27. However, any increase in the discharge pressurecauses a flow into cylinder 29 and correspondingly any sudden decreasein pressure in the discharge of the the fluid output thereof causes aflow of fluid out of said cylinder. Therefore, in normal operation,whether in'the high or low pressure range, supplementary feeder 25 mayact to offset operation of valve mechanism 6 in conjunction" withsupplementary feeder 25. This is accom-.

any sudden demand upon the fluid volume output of pumps 9 and I1.

A further increase of the pressure output of the hydraulic power systemduring operation in the high pressure range maybe had by suitableplished by charging said feeder as above described and causing thepressure in said feeder to become equal to the discharge pressure ofsaid-pumps. Then, if a further pressure demand is made upon said pumps,valve mechanism 6 may be so designed as to respond to the increasedFeeder 25 comprises a.

As a result, the fluid' discharge pressure built up by the pumps to meetthis increased demand, and automatically cut off conduits and 26 fromconduits I and 21, respectively, and opens conduit 21 to conduit 1,

. thereby feeding the suction side of pump 9 with a fluid of a pressureequal to the discharge 1 pressure of said pumps at the time valve 6 isoperated and thereby increasing the operating range of said pumps. 4

Thus, whenoperating to give the greatest possible pressure range, thehydraulic power unit operates with pumps 9 and I! connected in paralleland fed by the fluid from source 4 and with supplementary feeder 25being charged by the discharge fluid of said pumps. Upon anysudactuatedby the increased pressure of the pump to, meet this demand andrearranges the connection between said pumps, connecting the same inseries as previously described in detail. As the multi-stage operationof pump units 5 and I1 begins, valve mechanism 6 is so chosen that thefluid circuit is fed by source 4 and supplementary feeder 25 is' chargedby the high pressure discharge of pumps I1 and 9 in series and the samewill continue to be so charged until a still further pressure demandbrings said feeder into the fluid circuit to feed the suction. side ofpump 9 and thereby increase the discharge pres sure of pumps I7 and 9 inseries. The last step is performed as follows:

Referring to the valve 6 of Fig. 2 and assuming that a pressure slightlyabove the minimum output of pumps 9 and IT in series is required byservomotor i8. The discharged pressure of the two pumps at this valuewill be lead by conduit 26 through the port 33 in piston 32 to chamber34. This pressure will be exerted against piston 32 to move the same tothe right against the force of spring 31. The connection betweenconduits ii and l is not broken, however, until conduits 21 and l areconnected bythe shift of the piston 32. At this time the pressure inchamber 34 forces the piston 32 to shut off the communication of conduit5 so that source 4 no longer feeds the pumps. An initial pressureslightly above the minimum pressure of the pumps in series is then fedfrom the feeder 25 by way of conduits I and 21 to the inlet of pump 9.

There is thus provided a novel hydraulic power system which is adapted,for example, for actuating the retractable landing gear of an airplaneand which, as a complete unit, weighs'less than the' pumping unit, atpresent employed in airplanes for this purpose. There is, furthermore,provided a novel arrangement of a plurality of pumps, a supplementaryfeeder, and novel automatic control means therefor, whereby a wide dendecrease in output pressure, due to sudden thespirit and scope of theinvention. For a definition of thelimits 'of the invention, referencewill be had primarily to the appended claims.

What is claimed is:

1. In apparatus of the class described, a servomotor, a plurality ofpumps in parallel, a conduit connecting said pumps to said servo-motor,valve mechanism operatively controlled by the discharge pressure of oneof said'pumps and adapted to change the fluid connections between saidpumps causing a series arrangement of the latter, I

a reservoir of fluid, a second conduit connecting said reservoir to saidpumps, valve means controlling the fluid flow through said second-namedconduit, and a supplementary feeder normally connected through saidvalve means to said first-.

named conduit and adapted to be disconnected therefrom by said valvemeans at a predetermined pressure output of said pumps whereupon saidfeeder is placed in communication with said second-named conduit.

2. In apparatus ofthe class described, a fluid reservoir, a plurality ofpumps fed from said reservoir, conduit means connecting said pumps toact in parallel, a servo-motor fed by said pumps, means in the dischargeend of one of 'said pumps operative to cause a series arrangement ofsaid pumps when the pressure in said dischargereaches a predeterminedamount, and

means connected in the discharge end of said pumps whereby upon afurther increase in presrange of pressure outputs may be obtained duringsubstantially full load operation of the pumps.

Although only a single embodiment of the invention has been illustratedand described in detail, it is to be expressly understood that the surein the discharge end of said pumps the latter are disconnected from saidfluid reservoir and the pressure input at the inlet of said one pump isincreased.

3. In apparatus of the class described, a fluid reservoir, a pluralityof fluid pumps arranged in parallel and being normally fed from saidreservoir, means comprising a valve responsive to the pressure demandupon said pumps for increasin the pressure output thereof by varying theconnection of saidpumps to a series arrangement, and means for furtherincreasing the pressure output of said pumps, said last-named meanscomprising a supplementary feeder normally fed by the output of saidpumps and a valve mechanism interposed in the output of said pumps andoperative when the pressure in the Pump output reaches a predeterminedamount to disconnect said pumps from said fluid reservoir and to connectsaid feeder with the input of the first of said pumps when the latterare in series arrangement.

4. In apparatus of the class described, a fluid reservoir, a pluralityof fluid pumps arranged to operate in parallel and fed from saidreservoir means responsive to the pressure demand upon said pumps forincreasing the pressure output thereof by varying the. connections ofsaid pumps from a parallel to a series arrangement, a supplementaryreservoir in the output side of said pumps normally fed by said pumps,and valve means connecting said last-named reservoir to the output sideof said pumps whereby upon a predetermined increase in the pressureinthe output side of said pumps said valve means act to cut off said pumpsfrom said first-named reservoir and to place said last-named reservoirin communication'with the input of the first of said pumps when thelatter are in series arrangement.

5. In apparatus of the class described, a servomotor, pumpingmeansadapted to operate in parallel, a conduit connecting said pumping meansto said servo-motor, a, pressure controiied valve operatively, connectedto said pumping means and adapted to change the fluid connections to aseries arrangement for said pumping means, a fluid reservoir. asecondconduit connecting said reservoir to said pumping means, valve meanscontrolling the fluid flow from said reservoir, and a supplementaryfeeder connected to said second-named conduit through said valve means,said valve means operating upon the attaming ot-a predetermined pressurein the second-named conduit to cause said feeder to supplant saidreservoir as a fluid source.

KARL WILF'RID FIEBER,

